Featured image in Watson theme

Always when I add a featured image to my post it is scaled up to 550+ pixels (from 492 px) in the featured section of the front page - that´s maybe understandable as it should fit into the space.

But when I click on this article and it opens in a new window, the featured image above the article is now scaled up to 620+ pixels - and this is obviously to wide for the article, which has a smaller width than 620 px. Furthermore my featured image is then scaled from 492 px to more than 620 px and this looks awful.

Where is the mistake? How can I influence the size of the featured image in the article view?